December 2016 Archives

Being an arcade collector, I enjoy a variety of hard-to-find games, some JAMMA, some JVS, but all of them not terribly easy to play unless you have a spare cabinet around with a compatible control panel. Earlier this year, I set out on the task of building my own supergun: a generic term for an adapter that provides the power commonly used by arcade games (generally just +12/+5v, but sometimes -5v is needed) as well as converts the video, audio and control signals used. The result worked, but my control panel was raw, to say the least (laser cut by a friend on a single sheet of acrylic: I had no means to support it, the buttons had an odd spacing, and the acrylic chosen was slightly too thick for the buttons to clip in properly). Also, I relied on a chain of adapters. Power supplies are hard to get right, so I used an ATX power supply to provide +12v and +5v (note that current revisions of ATX remove -5v; to create this voltage, I used an isolating DC-DC converter that outputs 5v, with the positive output connected to ground). Similarly, I have games that sync at any of the three common refresh rates: while the vast majority use 15kHz, I have a few 31kHz and a few 24kHz. 15kHz is easy to convert, since it's relatively close to NTSC (and there are dedicated ICs for this purpose), but the other refresh rates are a bit more challenging. As a result, I decided to use a Gonbes GBS-8220 to convert the video signal. Sure, it may not be perfect, but the quality is quite decent, the board is readily available at low cost, and the result is a nicely upscaled VGA picture. Ultimately, this resulted in a mess of adapters, and while the resulting project was fun, it was by no means easy to carry with me (the original goal), nor was it convenient to use.

Enter the Combo AV EX+: an all-in-one JAMMA to VGA or HDMI adapter with a host of options. The standard configuration from TOPS (a Japanese distributor of used games and control boxes) comes with a two player, twelve button configuration using Seimitsu joysticks. I'm not a die-hard Sanwa fan, so saving a bit of money here seemed okay. The control panel itself is beautifully constructed: the case is stainless steel, the control panel is professionally cut out of a nicely patterned plastic, the positioning of the buttons and sticks are compact, but spaced enough to remain comfortable. The controller also features an internal speaker and 3.5mm jack. Internally, the wiring is nicely constructed. The buttons use quick connects (so, if you later want to upgrade to Sanwa buttons, it is easily accomplished), and the parts are largely commercially available. Internally, the VGA is converted using the same GBS-8220. The HDMI is converted from that, with what appears to be a VGA2HDMI PCB. There's also an RGB output for video, but using this requires disconnceting the input to the GBS-8220 to switch it over. Finally, there appears to be an option to also output composite and S-Video; this appears to take advantage of the GBS-8100. The power supply is a DIN rail style power supply, common to most arcade machines (note that there are some power supplies that are exclusively 12v or 5v; in this case, the three voltages are converted internally). Finally, there's a custom I/O board that is able to do rapid-fire on any of the 12 buttons. The delay is selectable, as are the buttons the rapid-fire assigns to, although I have not used this functionality.

Use is simple: plug in the JAMMA connector to the board (although most boards have the JAMMA connector recessed slightly, so using an adapter to handle this for you) is probably the best bet. Plug in the power video and switch the power on. Volume is controlled on the back via a knob, although there are two switches on the back related to the A/V output. A slider switch selects the audio output: HDMI or the internal speaker. A small rocker switch provides power to the HDMI output. The two larger black buttons provide coin input for P1/P2, and the smaller black button is wired to the test switch. 24mm start buttons for each player are also provided, just above the 6 buttons for that player.

Now, for the problems. First, shortly after receiving the unit, I found that the internal speaker eventually stopped functioning entirely. I traced this down to the volume knob reading a much higher resistance than it should have been. Normally, the volume knob should read approximately 0-100 ohms; we were almost a factor of 200 off from that (20 kOhm). Additionally, this is not exactly a standard part: it's a 100 ohm B-scale potentiometer. Thankfully, the manufacturer was able to provide a replacement through TOPS, and it was fairly simple to replace myself. A word of caution here: I'd avoid making any changes to the audio while the game is on, and operate both the board and internal speaker levels at a conservative volume: note that every game under the JAMMA standard outputs powered audio for an 8 ohm speaker in the cabinet. This is a much lower impedance than the high-Z inputs used by headphones and other hi-fi equipment (it's really just a small amplified speaker). Even the case uses a 10W rated 8 ohm speaker. Not sure if anything here was to blame, but better safe than sorry.

The second problem was related to the video: sometimes, in an intense game, the video would scramble, I'd lose a few frames, and it'd pick right back up. This took me a while to figure out was related to the Gonbes GBS-8220. At first, it looked like the game was losing sync. After some troubleshooting, though, I figured out the metal frame of the controller is common with earth ground, but the DC common output was isolated from this ground. However, whenever the post or shroud of the VGA connector would contact the metal frame nearby, the screen would jump, since suddenly the DC offset has changed. Eventually, I just worked around this issue by keeping the DC common at the same level as the earth ground by using a short jumper wire. Not the prettiest solution, but I figured it's nicer than the video signal serving the same purpose. (An alternative would have been to insulate everything with tape, but this looked like it might pose its own unique challenges.

Overall, I've been quite impressed with the quality of the controller. It functions as advertised, is quite solidly built, and the harness I'm using has a built-in kick harness for games that support it. Combine this with some excellent support, and I'm satisfied with such a high quality product.